1. Field
Example embodiments relate to a digital direct conversion receiving apparatus and method.
2. Description of the Related Art
When a Radio Frequency (RF) signal which is an analog signal is received, a sampling frequency which is at least twice a carrier frequency is required to enable an existing sampling theory to be applied. In general, however, a bandwidth where a signal exists may be 0.003 to 0.2% of a carrier frequency. Accordingly, a sampling scheme based on a carrier frequency may be ineffective and affect a digital domain due to a significant amount of data.
A Band-Pass Sampling (BPS) scheme has been provided to overcome such disadvantages. In a BPS scheme, a sampling frequency may be determined by a bandwidth of a signal without depending on a carrier frequency. Accordingly, an effective system may be structured. A BPS scheme digitally processes an input signal, using a small bandwidth and may be referred to as a digital direct conversion scheme or an RF direct conversion scheme. Also, the BPS scheme may be referred to as a band-pass sampling, a harmonic sampling, or a sub-sampling.
A digital direct conversion scheme may generate an aliasing by applying a lower sampling frequency, and have a sampling rate based on a bandwidth of a signal including information. A digital direct conversion scheme may be applied to a configuration of a receiving apparatus based on an analog down-conversion function being replaced with sampling. Also, a digital direct conversion scheme may perform sampling with respect to a signal received through an antenna, directly after passing a Low Noise Amplifier (LNA). Accordingly, an inexpensive and small wireless receiving apparatus may be provided.
A 1st-order BPS receiver may down-convert a signal, corresponding to an integer-position between a carrier frequency and a signal bandwidth, at a minimum sampling rate (fS=2B) being twice a bandwidth (B). Also, a 1st-order BPS receiver may down-convert a signal, corresponding to a non-integer position between a carrier frequency and a signal bandwidth, at the minimum sampling rate (fS>2B) greater than twice the bandwidth. However, since a sampling frequency (fS) may vary depending on a location of a signal band, the 1st-order BPS receiver is required to change the sampling rate depending on a bandwidth of a signal and a location of a band for universal access. Also, a bandwidth of an RF filter is to be varied.
A 2nd-order BPS receiver may remove an aliasing through a signal processing, after sampling a signal with a time delay using two paths to overcome the above-described disadvantages. Accordingly, the 2nd-order BPS receiver may select a sampling rate without considering the aliasing, and thereby may select a minimum sampling frequency identical to a bandwidth of a signal.
However, when a sampling rate of an input stream is identical to a bandwidth (B), an interpolant of a 2nd-order BPS receiver may reproduce a sample at the sampling rate of B, and thus an aliasing may be generated. Accordingly, a 2nd-order BPS receiver may be operated in only integer positions, and may be required to reconfigure an interpolant depending on a location of a signal band.